Digital audio equipment such as Compact Disc (CD), Digital Audio Tape (DAT), a multimedia system, or a digital telephone network are commonly used for high-quality transmission, reproduction, and processing audio signals in the form of digital audio signals. These digital audio signals are comprised of a series of numbers that represent an analog audio signal at successive instants of time. Digital audio signals can be manipulated using current digital signal processing (DSP) technology to achieve very powerful processing functions that are not available for analog audio signals, and digital audio signals are much less susceptible to noise in both wired and wireless transmission techniques. Thus, digital audio signals can be transmitted across very noisy transmission media and suffer no loss of information, as the receiver must only determine whether a one or a zero was transmitted in order to recover the digital information from the digital audio signal.
Transmission of digital information is known. In some cases of digital information transmission, the digital information is transmitted as a data stream synchronous to a data stream clock. In many cases, the data stream clock is not known in the system that is receiving the transmitted digital information, thus making the data stream asynchronous to the receiving system and more difficult to recover.
A common prior art solution used to recover the digital information from the asynchronous data stream is to recover the data stream clock by making a part of the receiving system synchronous to the data stream. To make the receiving system synchronous to the data stream, an analog phase-locked-loop (PLL) is added to the receiving system. The analog PLL generates a recovered clock whose frequency matches that of the data stream clock and maintains the accuracy of the recovered clock via feedback. While analog PLLs can accurately recover the data stream clock, it is not without costs. For example, analog PLLs can require a relatively large amount of additional analog circuitry, which increases both the size and complexity of the receiving system. In a digital integrated circuit application, the additional analog circuitry may require significant die area and additional process steps. In addition, the functionality of the analog PLL may be susceptible to noise from the digital system, which can result in errors.
Therefore, a need exists for a method and apparatus that extracts data, or digital information, from an asynchronous data stream while minimizing the additional analog circuitry, cost, and susceptibility to noise.